Tubifex is a cosmopolitan genus of tubificid annelids that inhabits the sediments of lakes, rivers and occasionally sewer lines. At least 13 species of Tubifex have been identified, with the exact number not certain, as the species are not easily distinguishable from each other. Reproduction Tubifex worms are hermaphroditic: each individual has both male (testes) and female (ovaries) organs in the same animal. These minute reproductive organs are attached to the ventral side of the body wall in the celomic cavity. In mature specimens, the reproductive organs are clearly found on the ventral side of the body. Copulation and cocoon formation Although the Tubifex worms are hermaphrodites, the male and female organs become mature at different times; thus self-fertilization is avoided, and cross-fertilization is encouraged. Two mature Tubifex worms undergo copulation by joining ventral and anterior surfaces together with their anterior ends pointing opposite directions. Thus, the spermathecal opening of each worm is nearer to the male apertures of another worm. The penial setae of one worm penetrate into the tissues of other worm and thus the conjugants are held together. At this stage, the sperm of one worm is passed into the spermathecae of the other worm. After copulation, they separate and begin to produce egg cases containing eggs, called cocoons. The cocoon is formed around the clitellum as a soft, box-like structure into which the ova and the sperm are deposited. Soon, the Tubifex worm withdraws its body from the egg case by its backward wriggling movements. Culturing Tubifex Tubifex are raised commercially, mainly for fish food: the reddish Tubifex tubifex. Tubifex can be easily cultured on mass scale in containers with 50- to 75-mm thick pond mud at the bottom, blended with decaying vegetable matter and masses of bran and bread. Continuous, mild water flow is to be maintained in the container, with a suitable drainage system. After the arrangement of the system, the container is inoculated with Tubifex worms which can be obtained from nearby muddy canals or sewage canals. Within 15 days, clusters of worms develop and can be removed with mud in masses. When worms come to the surface due to lack of oxygen, they are collected and washed under brisk stream of water to remove residual mud attached to their bodies. Live food Tubifex worms are often used as a live food for fish, especially tropical fish and certain other freshwater species. They